1. Field of the Invention
The invention concerns radio-therapy and, more particularly, in a radio-therapy machine, a system and a method for measuring and checking the position of a patient.
2. Description of the Prior Art
Radio-therapy treatment is decided on the basis of a whole set of information of a diagnostic type, essentially comprising information on the nature, extent and location of the tumor and information on the general state of the patient. The treatment is defined by a program of treatment which is drawn up so as to give a prescribed dose of radiation to the volume of the tumor and the smallest possible dose to tissues that do not form part of the volume of the tumor. To this effect, the treatment program defines the nature, intensity, orientation and extent of the beams which will be used to irradiate the patient, and is drawn up on the basis of geometrical data given by a simulator and results of computations of doses given by a specialized data processing system.
The radio-therapy simulator essentially consists of a radiology apparatus using X-rays, which reproduces the geometry of the radio-therapy apparatus but uses a diagnostic type of X-ray source, namely one with low energy compared with that of the high energy radiation source of the radio-therapy apparatus. This radio-therapy apparatus is associated with an imaging system used to display the organs and tissues that the X-ray beam goes through.
To treat the tumor, it is necessary to have precise knowledge of its position with respect to the radiation source. For this purpose, the simulator has several optical means to identify the relative position of the patient and the radiology apparatus. One of these means is a telemeter designed to measure the distance between the X-ray source and the point at which the axis of the X-ray beam enters the patient's body. This distance is called the source-skin distance.
As shown in FIG. 1, a telemeter of the type used in a radio-therapy simulator has a first light source which projects the shadow of a cross 2 on a patient 7. The light source 1 is merged with the X-ray source and the point of intersection of the two arms of the cross 2 is located on the axis of the beam X. The point 3, the projected shadow, on the patient's skin, of the intersection point of the two arms of the cross 2, is therefore merged with the point at which the axis of the beam X enters the body of the patient 7.
The telemeter also has a second light source 4 which projects the shadow of a graduated scale 5 on the patient 7. The source 4 and the axis of the graduated scale 5 are in the same plane as the axis of the X-ray beam and the result thereof is that the axis of the shadow 6 of the graduated scale 5 goes through the point 3.
The point marking the shadow of the graduated scale 5, which coincides with the point 3, depends on the distance between the source 1 and the point 3 so that the observation of this marker point in coincidence with the point 3 thus gives a measurement of the source-skin distance.
The data used by a computer system to compute the doses comprises, firstly, the geometry and the nature of the beams and, secondly, information on the patient's anatomy in the region exposed to the radiation.
The anatomical information is generally given in the form of images representing the density of the patient's tissues in the coronal sections of the patient. The images of these sections are given by several means:
the radiology apparatus of the simulator which gives views at a variety of angles of incidence; PA1 a tomodensitometer which gives information on the nature of the tissues and; PA1 a conformator or shape plotting apparatus which gives readings of the external contour of the patient in different sectional planes. PA1 simulation systems: PA1 a) a scanning of at least one part of the surface of the patient's body by a light beam, the source of which is merged with the radiation source so as to surface of the patient's body; PA1 b) a detection of these points of impact by the recording of an appropriate image; PA1 c) a computation of the position of these points of impact using the knowledge of the position of the source and the position, on the image, of these points of impact; PA1 d) a recording of the positions of these points of impact with respect to the corresponding positions of the light beam that has given rise to them. PA1 e) scanning the patient's body by the light beam using information on recorded positions of the light beam to obtain the points of impact for which the positions have been recorded; PA1 f) measuring the real position of these points of impact in implementing the operation a), b), c) and d). PA1 g) comparing the real positions of the points of impact with the recorded position, and, PA1 h) moving the patient's body so that the real positions coincide with the recorded positions.
FIG. 2 enables an understanding of what a conformator consists of. It has a tracer 10, the tip of which can move only in a plane defined by two moving rails 12 and 13. This plane is brought into coincidence with the plane of the section for which it is sought to plot the external contour. The tracer 10 is provided, at the end opposite its tip 11 with a pencil 14 designed to trace points on a sheet of paper 15 placed in a plane parallel to the section plane. It will be understood that, by construction, the movement of the pencil 14 is deduced, by translation, from that of the tip 11. Thus, to read an external contour 16, the tip 11 of the tracer 10 is brought into contact with some significant positions on the skin of the patient 7 and, for each of these positions, a point is traced by the pencil 14 on the sheet 15.
The various operations that have just been briefly described enable the radio-therapy treatment program to be drawn up. To implement it, it is necessary to define the relative position of the different X-ray beams, stipulated by the treatment, with respect to the patient's body. This is obtained by drawing indelible marks on the patient's skin so as to indicate the contour of each X-ray beam. To enable these various marks to be drawn, the X-ray beams are displayed by optical means called delineators.
A delineator (FIG. 3) consists of a light source 21, placed at the point of origin of the X-ray beam which projects the shadow of a diaphragm 22 on the patient's skin. The shape of the diaphragm is such that its projection 23 on the patient's skin represents the plotting of the entrance of the X-ray beam into the patient and is used to draw the identifying marks on the patient's skin.
The diaphragm 22 usually consists of a set of movable plates, with rectilinear edges when the beam is rectangular, or a specially cut plate when the beam has a more complex shape.
When the operations that have just been described are over, the patient can be treated in a radio-therapy installation. The first operation of the treatment consists in placing him in a position that corresponds, as far as possible, to the one he had in the simulator. To this effect, this radio-therapy installation has several optical means corresponding to those of the simulator, in particular the telemeter.
Before the patient is subjected to irradiation, the position of the therapeutic beams with respect to the patient is verified with a delineator identical to that of the simulator so as to make sure that the light trace thus obtained corresponds to the marks made on the patient's skin.
The following are the main drawbacks of prior art
The measurement of the source/skin distance requires the presence of an operator near the patient to observe the light traces projected by the telemeter. The result thereof is a loss of time and risks of making mistakes. But, above all, the measurement cannot be made during the irradiation because the operator cannot stay near the patient. This means that involuntary movements by the patient are not detected and may thus result in irradiation that is not according to the irradiation program.
The plotting of the external contour of a section of the patient, using a conformator, is a slow operation that lacks precision and calls for the presence of an operator near the patient. It therefore cannot be done during irradiation. This prevents its use as a supplementary means to ascertain that the treatment is with inaccordance with the treatment program.
The program of optical delineation is fast only when the beam has a rectangular section. In the most complicated cases, specific diaphragms have to be made and this is a slow process.
An aim of the present invention, therefore, is to make a system, for the measurement and checking of a patient's position, that does not have the above-mentioned drawbacks of prior art systems, and which fulfils the functions of the telemeter, the conformator and the delineator described above.